A new class of low temperature initiators has been found, CnF2n+1(CH2)aCF2(Cxe2x95x90O)Oxe2x80x94O(Cxe2x95x90O)CF2(CH2)bCmF2m+1, wherein n and m are each independently 1 to 4, and a and b are each independently 1 or 2, enabling fluoroolefin polymerizations at relatively low temperatures.
Diacyl peroxides of diverse structure have been patented as fluoroolefin polymerization initiators, for example,
[RO(CH2CF2CF2O)nCH2CF2(Cxe2x95x90O)Oxe2x80x94]2, U.S. Pat. No. 4,663,407, issued May 1987, to Daikin Industries,
[xe2x80x94O(Cxe2x95x90O)CFRf(C3F6O)h(C2F4O)m(CF2O)n(CgF2gO)aCFRf(Cxe2x95x90O)Oxe2x80x94]x, U.S. Pat. No. 3,882,193 (issued May 6, 1975 to Minnesota Mining and Manufacturing Company); [X(CF2)n(Cxe2x95x90O)Oxe2x80x94]2, U.S. Pat. No. 3,528,954 (issued Sep. 15, 1970 to E.I. du Pont de Nemours and Company); XCmF2m(Cxe2x95x90O)OO(Cxe2x95x90O)CnF2nX, EP 0606 492 A1 (published Jul. 9, 1993, to Daikin Industries) and
Cl2FC(Cxe2x95x90O)OO(Cxe2x80x94O)CCl2F U.S. Pat. No. 5,569,728 (issued Oct. 29, 1996, to Ausimont, SpA.). The best diacyl peroxide for a particular application can often be determined by its half-life. By xe2x80x9chalf-lifexe2x80x9d we mean the elapsed time it takes for half of the initiator in a system to decompose thermally to radicals. An initiator needs to last long enough for homogeneous mixing to occur with monomer but not so long as to make polymerization uneconomically slow. Half-lives on the order of 15 minutes to several hours are desirable.
Polymerization temperature can affect fundamental aspects of final polymer structure such as molecular weight and branching. Thus, a preferred polymerization temperature is chosen first and an initiator with an appropriate half-life chosen second. As used herein xe2x80x9cHFPO is hexafluoropropylene oxide. For example were a polymerization""s temperature set to 30xc2x0 C., dimer peroxide (DP) with a half-life of 0.98 hours would be a faster and better choice than heptafluorobutyryl peroxide (4P) with a half-life of 8.8 hours (Table 1). If, however, the same polymerization needed to be run at 0xc2x0 C., the half-life of DP would increase to 64 to 92 hours (Table 1), threatening an uneconomically slow process.
The potential advantages of faster, lower temperature initiation include increased productivity, increased polymer linearity, decreased chain transfer, increased polymer molecular weight, decreased monomer oligomerization during product letdown, decreased acid fluoride end group formation in the polymer, and decreased reactor pressure in condensed media such as liquified hexafluoropropylene (HFP) or CO2. The fastest (i.e., lowest temperature), well documented prior art diacyl peroxide, 1H3P, has a 16 hour half-life at 10xc2x0 C. (see Table 1, J. Org. Chem., 47, 2009 (1982) and Japanese Pat. 61152653 A2, Chem. Abstracts 106:120380). Trichloroacetyl peroxide, which has been reported to have a 10 hour half-life at xe2x88x923.9xc2x0 C. (see U.S. Pat. No. 5,688,838) is still faster than 1H3P (xe2x80x9cHCF2CF2xe2x80x94xe2x80x9d) but has two disadvantages. First, the xe2x80x94CCl3 group tends to chain transfer and, second, the initiating Cl3C* radical remains attached to the polymer chain as a potentially unstable end group. At 10xc2x0 C., the inventive bis(2,2,5,5,5-pentafluoropentanoyl) peroxide (hereinafter xe2x80x9c4H5Pxe2x80x9d) and bis(2,2,5,5,6,6,7,7,8,8,8-undecafluorooctanoyl) peroxide (hereinafter xe2x80x9c4H8Pxe2x80x9d) initiators disclosed herein are 13 times faster and 9 times faster, respectively, than 1H3P. Holding the rate of radical generation constant, this represents a 10xc2x0 C. to 20xc2x0 C. advantage in polymerization temperature for the inventive peroxides of the present invention. Unlike trichloroacetyl peroxide, 4H5P and 4H8P will not introduce undesirable chlorine into either the polymer or the reaction mixture. Thus 4H5P, 4H8P, and the related peroxides disclosed herein appear particularly attractive as low temperature fluoroolefin polymerization initiators.
Commonly owned U.S. Pat. No. 5,763,552 discloses partially fluorinated surfactants of the formula Rfxe2x80x94(CH2)mxe2x80x94Rxe2x80x2fxe2x80x94COOM useful in the polymerization of fluorinated monomers. These surfactants are synthetic precursors, several steps removed, for many of the diacyl peroxides disclosed herein.
Disclosed in this invention are diacyl peroxides having the structure I,
RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)OO(Cxe2x95x90O)CF2CWWxe2x80x2(CZZxe2x80x2)exe2x80x2Rfxe2x80x2xe2x80x83xe2x80x83I
wherein e and exe2x80x2 are independently 0 or 1; and
when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2 is H or F; when exe2x80x2=0, at least one of W, Wxe2x80x2 is H and any of the other W,
Wxe2x80x2 is H or F;
when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F;
when exe2x80x2=1, at least one of W, Wxe2x80x2, Z, Zxe2x80x2 is H and any of the other W, Wxe2x80x2, Z, Zxe2x80x2 is H or F;
wherein Rf=CnF(2n+1), n=1 to 4; and
wherein Rf=CmF(2m+1), m=1 to 4.
Also disclosed is a method for preparing a new class of diacyl peroxides, comprising:
contacting at least one acid halide of the formula II
RCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)Lxe2x80x83xe2x80x83II
wherein e=0 or 1, and when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2is H or F, and when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F;
wherein L is Cl or F, and
wherein R is Rf or Rfxe2x80x2; and wherein Rf=CnF(2n+1), n=1 to 4 and Rf=CmF(2m+1), m=1 to 4;
with a peroxide, to generate a diacyl peroxide of the structure
RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)OO(Cxe2x95x90O)CF2CWWxe2x80x2(CZZxe2x80x2)exe2x80x2Rfxe2x80x2xe2x80x83xe2x80x83I
wherein e and exe2x80x2 are independently 0 or 1; and
when e=0, at least one of X, Xxe2x80x2 is H and any of the other X,
Xxe2x80x2 is H or F; when exe2x80x2=0, at least one of W, Wxe2x80x2 is H and any of the other W, Wxe2x80x2 is H or F;
when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F;
when exe2x80x2=1, at least one of W, Wxe2x80x2, Z, Zxe2x80x2 is H and any of the other W, Wxe2x80x2, Z, Zxe2x80x2 is H or F;
wherein Rf=CnF(2n+1), n=1 to 4; and
wherein Rfxe2x80x2=CmF(2m+1), m=1 to 4.
A further disclosure of this invention is a method for using a diacyl peroxide of the structure I, comprising:
RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)OO(Cxe2x95x90O)CF2CWWxe2x80x2(CZZxe2x80x2)exe2x80x2Rfxe2x80x2xe2x80x83xe2x80x83I
wherein e and exe2x80x2 are independently 0 or 1; and
when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2 is H or
F; when exe2x80x2=0, at least one of W, Wxe2x80x2 is H and any of the other W, Wxe2x80x2 is H or F;
when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y,Yxe2x80x2 is H or F;
when exe2x80x2=1, at least one of W, Wxe2x80x2, Z, Zxe2x80x2 is H and any of the other W, Wxe2x80x2, Z, Zxe2x80x2 is H or F;
wherein Rf=CnF(2n+1), n=1 to 4; and
wherein Rfxe2x80x2=CmF(2m+1), m=1 to 4
(i) contacting at least one diacyl peroxide having the structure I with a monomer;
(ii) optionally, in the presence of a reaction medium selected from the group consisting of fluorocarbon, chlorofluorocarbon, and hydrocarbon fluids; fluorocarbon, chlorofluorocarbon and hydrocarbon mixed with water, wherein hybrid polymerization conditions form; and liquid or supercritical carbon dioxide; and
(iii) polymerizing the monomer, under suitable polymerization temperature and pressure whereby fluoroolefin polymerization occurs.
Another disclosure of this invention is a process for fluoroolefin polymerization, comprising the steps of:
(i) contacting at least one diacyl peroxide having the structure I
RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)OO(Cxe2x95x90O)CF2CWWxe2x80x2(CZZxe2x80x2)exe2x80x2Rfxe2x80x2xe2x80x83xe2x80x83I
wherein e and exe2x80x2 are independently 0 or 1; and
when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2 is H or F; when exe2x80x2=0, at least one of W, Wxe2x80x2 is H and any of the other W, Wxe2x80x2 is H or F;
when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F;
when exe2x80x2=1, at least one of W, Wxe2x80x2, Z, Zxe2x80x2 is H and any of the other W, Wxe2x80x2, Z, Zxe2x80x2 is H or F;
wherein Rf=CnF(2n+1), n=1 to 4; and
wherein Rfxe2x80x2CmF(2m+1), m=1 to 4;
with a monomer;
(ii) optionally, in the presence of a reaction medium selected from the group consisting of fluorocarbon, chlorofluorocarbon, hydrocarbon fluids; fluorocarbon, chlorofluorocarbon and hydrocarbon mixed with water, wherein hybrid polymerization conditions form; and liquid or supercritical carbon dioxide; and
(iii) polymerizing the monomer, under suitable polymerization temperature and pressure whereby fluoroolefin polymerization occurs.
This invention also discloses a product of the process for fluoroolefin polymerization, wherein said process comprises the steps of:
(i) contacting at least one diacyl peroxide having the structure I
RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)OO(Cxe2x95x90O)CF2CWWxe2x80x2(CZZxe2x80x2)exe2x80x2Rfxe2x80x2xe2x80x83xe2x80x83I
wherein e and exe2x80x2 are independently 0 or 1; and
when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2 is H or F; when exe2x80x2=0, at least one of W, Wxe2x80x2 is H and any of the other W, Wxe2x80x2 is H or F;
when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F;
when exe2x80x2=1, at least one of W, Wxe2x80x2, Z, Zxe2x80x2 is H and any of the other W, Wxe2x80x2, Z, Zxe2x80x2 is H or F;
wherein Rf=CnF(2n+1), n=1 to 4; and
wherein Rfxe2x80x2=CmF(2m+1), m=1 to 4;
with a monomer;
(ii) optionally, in the presence of a reaction medium selected from the group consisting of fluorocarbon, chlorofluorocarbon, hydrocarbon fluids; fluorocarbon, chlorofluorocarbon and hydrocarbon mixed with water, wherein hybrid polymerization conditions form; and liquid or supercritical carbon dioxide; and
(iii) polymerizing the monomer, under suitable polymerization temperature and pressure whereby fluoroolefin polymerization occurs.
This invention relates to the synthesis of a novel class of diacyl peroxides which are effective low temperature polymerization initiators for nonaqueous and hybrid polymerization conditions, including the use of CO2 as a polymerization solvent. By xe2x80x9chybrid polymerization conditionsxe2x80x9d is meant mixed aqueous and non-aqueous solvents. Disclosed in the invention are diacyl peroxides of the structure
RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)OO(Cxe2x95x90O)CF2CWWxe2x80x2(CZZxe2x80x2)exe2x80x2Rfxe2x80x2xe2x80x83xe2x80x83I
wherein e and exe2x80x2 are independently 0 or 1; and
when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2 is H or F; when exe2x80x2=0, at least one of W, Wxe2x80x2 is H and any of the other W, Wxe2x80x2 is H or F; when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F; when exe2x80x2=1, at least one of W, Wxe2x80x2, Z, Zxe2x80x2 is H and any of the other W, Wxe2x80x2, Z, Zxe2x80x2 is H or F;
wherein Rf=CnF(2n+1), n=1 to 4, preferably 1 or 4; and
wherein Rfxe2x80x2=CmF(2m+1), m=1 to 4, preferably 1 or 4.
These peroxides are synthesized from one or more acid halides of the formula
RCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)Lxe2x80x83xe2x80x83II
wherein e=0 or 1, and when e=0, at least one of X, Xxe2x80x2 is H and any of the other X, Xxe2x80x2 is H or F, and when e=1, at least one of X, Xxe2x80x2, Y, Yxe2x80x2 is H and any other of the other X, Xxe2x80x2, Y, Yxe2x80x2 is H or F;
wherein L is Cl or F, and
wherein R is Rf or Rfxe2x80x2 as described above.
For example starting with two different acid halides RfCXXxe2x80x2(CYYxe2x80x2)eCF2(Cxe2x95x90O)L gives not only the two symmetrical peroxides but the unsymmetrical peroxides as well. The acid chlorides or acid fluorides are subsequently reacted with peroxides such as, but not limited to, H2O2 in the presence of a base, Na2O2, and K2O2 to form the desired peroxide compounds. Examples of useful bases are, but not limited to, NaOH, KOH, Na2CO3, and K2CO3. This is demonstrated in the Examples below. When increased peroxide solubility in the reaction solvent is desired, mixtures of two or more acid halides can be used. The product in such cases includes unsymmetrical peroxides.
The preparation of initiators of this invention can be facilitated by a variety of processes, including high intensity mixing processes as described in U.S. Pat. No. 5,831,131, incorporated herein by reference. High intensity ultrasonic mixing was used to make the peroxides of Examples 1B, 2B and 2C described below. One advantage of ultrasonic mixing is the simplicity and speed of the synthetic method. Other synthetic methods can also be used, including stirring as disclosed in Z. Chengxue et al., J. Org. Chem., 47, 2009 (1982), and making a nearly waterfree slurry as disclosed in U.S. Pat. No. 5,021,516. Any of the synthetic methods commonly used to make diacyl peroxides generally from acid halides can be used in the present invention. A general reference describing these methods is found in S. R. Sandler and W. Karo, Polymer Syntheses. Vol. 1, Academic Press, New York, 1974, Chapter 14.
Considering that 2, 3, 4, and 5, defined below in Table 2, decompose much faster than 4P 7, we conclude that having C-H bonds two or three carbons removed from the peroxide carbonyl greatly accelerates peroxide decomposition.
Vinyl monomers are generally useful for polymerization according to this invention. Preferably, these monomers are fluorocarbon, chlorofluorocarbon and hydrofluorocarbon vinyl olefins or vinyl ethers that homopolymerize, copolymerize, or copolymerize with hydrocarbon monomers such as ethylene and propylene, which are known to copolymerize with fluoroolefins. The monomers tetrafluoroethylene (TFE), perfluoropropylene vinyl ether) (PPVE), perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole(PDD), hexafluoropropylene (HFP), CF2=CFOCF2CF(CF3)OCF2CF2SO2F (PSEPVE) and CF2=CFOCF2CF2SO2R, vinylidene fluoride (VF2), vinyl fluoride, trifluoroethylene, CF2xe2x95x90CFOCF2CFCF3OCF2CF2CN (8-CNVE), chlorotrifluoro ethylene (CTFE), (CF3)2Cxe2x95x90CH2, and vinyl acetate (VAc) are most preferably employed.
A variety of polymer products can be formed from the monomers employed. These are well known to those skilled in the art. See, for example, Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition, Wiley-Interscience, New York, 1994, Vol. 11, pp. 621-729; H. Mark et al, Encyclopedia of Polymer Science and Engineering, 2nd edition, Wiley-Interscience, New York, 1987, Vol. 7, pp. 256-269 and 1989, Vol. 16, pp. 577-640; and J. Schiers, ed., Modern Fluoropolymers, John Wiley and Sons, New York, 1997.
The processes of this invention can take place in a variety of reaction media. These media include fluorocarbon, chlorofluorocarbon and hydrocarbon fluids; fluorocarbon, chlorofluorocarbon and hydrocarbon fluids mixed with water to form hybrid polymerization conditions; and liquid and supercritical carbon dioxide.
The diacyl peroxides of the present invention permit fluoroolefin polymerizations at lower temperatures. The initiation temperatures for the reactions of the present invention can range from about xe2x88x9220xc2x0 C. to 30xc2x0 C., preferably xe2x88x9210xc2x0 C. to 20xc2x0 C., and most preferably 0xc2x0 C. to 10xc2x0 C.
The polymerization process of the present invention offers a number of potential advantages, including increased productivity, increased linearity, faster reaction time, increased molecular weight, decreased monomer oligomerization during letdown, decreased acid fluoride end group formation, and decreased reactor pressure in condensed media such, as liquified HFP or CO2.
The peroxide titration Bused in the Examples follows. In a loosely stoppered Erlenmeyer flask several grams of dry ice are added to 25 ml of glacial acetic acid, so as to flush oxygen from the system. Five ml of a solution of 30 g of KI in 70 ml of deoxygenated water was added, and then 5.0 ml of the peroxide solution to be analyzed. The mixture was stirred for 30 minutes to allow the peroxide to react with the iodide. One hundred ml of deoxygenated water was added and the deep iodine color was titrated to light yellow with 0.1 N sodium thiosulfate. Then 0.5 g of xe2x80x9cThyodenexe2x80x9d (purchased from Fisher Scientific Co.) iodometric indicator was added making the reaction mixture turn blue. Titration was completed by bringing to a colorless endpoint with additional 0.1 N sodium thiosulfate. Molar peroxide concentration was calculated by multiplying 0.01 by the total number of ml of sodium thiosulfate solution.